Basically, this is a jelly of pigs head. The head, minus the brains, is boiled in salt water until the meat falls off, and then the resulting mix is rendered down to a jelly. Served cold with a salad or in a sandwich it's delicious.
One of those dishes that some feel are better eaten with the eyes closed. It can be disconcerting when you notice a bit of eyebrow in the jelly!
I am told beef brawn also exists.
Also known as pork cheese in East Anglia, fromage de tete de porc in France and head cheese in the USA.